Process for reforming heavy naphtha

ABSTRACT

THIS INVENTION RELATES TO A PROCESS FOR REFORMING HEAVY NAPHTHA WHEREIN A NAPTHTA FEED BOILING IN THE RANGE OF BELOW ABOUT 390*F. IS REFORMED IN A SERIES OF REACTORS WHILE A NAPHTHA FRACTION BOILING BETWEEN ABOUT 390* TO 415*F. IS ADDED TO THE FEED INTO THE LAST REACTORS OF THE SERIES. THE LAST REACTORS ARE PROVIDED WITH AN EXCESS OF HYDROGEN. THE INVENTION PROVIDES AN INCREASED AMOUNT OF REFORMATE OF INCREASED OCTANE. THE INVENTION ALSO PROVIDES FOR THE UPGRADING OF A HEAVY NAPHTHA FRACTION WITHOUT EXCESSIVE COKE FORMATION.

March 7, 1972 M. c. KIRK, JR.

' PROCESS FOR REFORMING HEAVY NAPHTHA Filed June 25, 1970 MERRITT C.KIRK JR. ERNEST W. DOBSON BY I AT RNEY DESULFURIZATION ZONE 3,647,679PROCESS FOR REFORMING HEAVY NAPHTHA Merritt C. Kirk, Jr., Thornton, andErnest W. Dobson, Westtown Township, Chester County, Pa., assignors toSun Oil Company, Philadelphia, Pa.

Filed June 25, 1970, Ser. No. 49,606

Int. Cl. Cg 39/00 [1.8. Cl. 208-63 2 Claims ABSTRACT OF THE DISCLOSUREThis invention relates to a process for reforming heavy naphtha whereina naphtha feed boiling in the range of below about 390 F. is reformed ina series of reactors while a naphtha fraction boiling between about 390to 415 F. is added to the feed into the last reactors of the series. Thelast reactors are provided with an excess of hydrogen. The inventionprovides an increased amount of reformate of increased octane. Theinvention also provides for the upgrading of a heavy naphtha fractionwithout excessive coke formation.

This invention relates to a process for reforming heavy naptha.Generally, naphtha fractions boiling in the range of about 200 to 390 F.are used as charge feed to reformers. The feed is prepared bydesulfurization and prefractionation of a 200 to 440 F. naphtha. Thedesulfurized fraction boiling above about 390 -F. is normally used injet fuel or kerosene. The latter fraction is undesirable reformer feedbecause it contains dicyclic naphthenes and Tetralins whichdehydrogenate to dicyclic aromatics which are high boiling coke formersof low octane number.

The present invention relates to a modified reforming process whichpermits the reforming of feed stocks boiling up to about the 415 F.range. In the process, desulfurized naphtha feed is separated into afraction with a boiling range below about 390 F., a fraction boiling inthe approximate range of 390 to 415 F. and a fraction boiling above 415F. The fraction of boiling range below about 390 F. is charged into amultiple reactor reformer and is reformed in the conventional manner.The 390 to 415 F. fraction is charged along with excess hydrogen intothe last reactors in the reformer. The excess hydrogen minimizes cokingfrom the increased hydrocracking in the last reactors which might haveoccurred on account of the presence of the 390 to 415 F. feed material.The present proposal takes advantage of the predominance of thishydrocracking reaction in later reforming stages which reaction ispredominant over the dehydrogenation of naphthenes which takes place,for the most part, in the first reforming stages. The promotion of thehydrocracking of the Tetralins and naphthenes in the heavy naptha toalkyl aromatic in preference to their conversion to naphthalenes resultsin the production of high octane low boiling gasoline components.

The invention is describable as an improvement to a process forreforming naptha in a multiple reactor reformer in which the processcomprises charging a naptha feed boiling below about 390 F. sequentiallyinto each reactor of the reformer to reform the feed, and recovering aproduct of increased octane number. The improvement comprises feeding anaphtha fraction boiling in the range of about 390 to 415 F. into laterreactors of the reformer in the presence of excess hydrogen to therebyincrease the amount of product of increased octane.

The present invention can be thought of as a reforming processcharacterized by altered conditions in its later stages as describedabove or the invention can be thought of as an integrated processcharacterized by a combination of two steps wherein the first stepcomprises dehydronited States Patent 0 "ice genation under reformingconditions and the second step comprises hydrocracking.

Angell, US. Patent No. 2,333,625 which issued Nov. 9, 1943, teachesthermal reforming a naphtha and hydrogenating the reformate in thepresence of a naphthenic oil hydrogen donor. Olefins of the reformateare saturated by the hydrogenation step. The objects of the Angellpatent are the reduction of the olefinic nature of reformate by aconversion which does not materially decrease the reformate anti-knockvalue and the provisions of an inexpensive hydrogen source to effectthis conversion. The Angell process does not seek to upgrade the addedhydrogen donor as a gasoline component.

Hemrninger, US. Patent No. 2,696,460 which issued Dec. 7, 1954,discloses a combination process for making gasoline in which a heavynaphtha is split into two streams. One stream is reformed and the otherstream (the heavier fraction) is subjected to thermal cracking andhydrogenation. Preferably, the cracking and hydrogenation processes areperformed in the same zone. By the invention, the tendency of heavierfraction to form coke in reforming is avoided. The lighter fraction,which is conventionally reformed is a to 320 or 350 F. fraction. Theheavier fraction boiling from about 350 up to 450 F. is cracked andreformed in combination with the lighter stream. The cracked heavierstream may be hydrogenated before being charged into the reforming zone.In the present invention, the heavier fraction need not be preliminarilycracked because its boiling range has been selectively chosen toeliminate that portion of the fraction which would need to be cracked tohigh octane gasoline precursors. The heavier fraction of the presentinvention can be charged directly into the latter stages of thereforming process thus taking advantage of predominating reactions whichtake place in these later stages to upgrade the heavier fraction withoutproducing excessive coking and without the requisite cracking of thefraction preliminary to charge to the reforming zone. The advantagesobtained by this combined process in simplicity of equipment andprocessing steps reflect the significant improvements obtained by thepresent invention.

M. Oblad, US. Pat. No. 2,703,308, Mar. 1, 1955, teaches a heavy naphthafraction hydrocracked to produce a high octane light gasoline fractionand a naphtha fraction of relatively poor octane quality which isreformed. Reformate from this latter step boiling below 400 F. is addedto the high octane fraction produced in the hydrocracking step.Reformate boiling above 400 F. is added to the feed to the crackingzone. This process requires a fractionation of the product from thereforming zone, to reform a fraction boiling up to 400 F., prior tohydrocracking in combination with the complete feed. The patent processeffects conversion of substantially the entire feed of a hydrocarboncharge stock of above gasoline boiling range to gasoline of high octanerating. The present invention preliminarily divides a heavy naphtha intotwo streams. The two streams can be then converted under conditions mostresponsive to their respective processing requirements.

Scott, US. Pat. No. 3,124,523, Mar. 10, 1964, proposes subjecting aheavy fraction boiling in the range of 180 to 550 F. or 250 to 450 F. toreforming followed by treatment with hydrogen in a crackingisomerization zone. The present invention, by subjecting only the lowerboiling portion of the heavy naphtha fraction to reforming, reduces theproblem of heavy coke formation which problem must inherently accompanythe reforming of the high range of the heavy naphtha fraction asproposed in the Scott patent.

If the present invention is described in terms of a two stage conversionprocess rather than as an improvement to reforming as described above,then the present invention comprises a process for producing gasolineemploying in combination a reforming zone and anisomerizationhydrocracking zone comprising separating a heavy naphthainto a first fraction boiling below about 390 F. and a second fractionboiling between about 390 F. and 415 F., reforming the first fraction inthe reforming zone under conditions which predominantly bring aboutdehydrogenation of naphthenes in the first fraction, adding the secondfraction to the product from the reforming zone and subjecting thecombined fractions to hydro cracking and isomerization in the presenceof excess hydrogen to produce a gasoline of improved octane number.

The drawing is a schematic flow diagram of the present invention.

The present invention will be described in detail with reference to thedrawing. A naphtha 1 such as a catalytically-cracked naphtha boilingbetween about 200 to 440 F. is desulfurized in 2 and then passed throughline 3 into a fractionation zone 4 where the naphtha is separated into afraction 5 boiling in the range above about 415 F., a 390 to 415 F.boiling range fraction 6, a 200 to 390 F. boiling range fraction 7, anda light end fraction boiling below about 200 F. The 200 to 390 F. cut istaken from the fractionator 4 and is reformed in reactor zonesrepresented by zones 9, and 11. The reforming of the 200 to 390 F.fraction is illustrative of the present invention but it should be notedthat other naphtha fractions can be reformed as part of the presentinvention so long as the fraction has a final boiling point which is atabout 390 F. or which is below 390 F. It should also be noted that thedrawing shows three reforming zones as specifically exemplary of thepresent invention, but the process of the invention can be conducted intwo or even one reactor with two contiguous zones or in more than tworeactors.

Broadly, in the present invention the naphtha fraction boiling belowabout 390 F. is passed into a reforming zone provided with a reformingcatalyst which can be any catalyst known in the art for reforminghydrocarbon fractions. For example, the catalyst can be any of theplatinum-on-alumina or rhenium-platinum-on-alumina catalysts whichgenerally contain between 0.1 to 2.0 percent platinum. Catalysts of thistype are available commercially and are extensively described in theliterature. The catalyst compositions can include various active formsof alumina, such as gamma, eta, and kappa, and the alumina may varyconsiderably in surface characteristics depending upon how the catalystwas made. The combination of platinum and the alumina produces acatalyst having a plurality of functions whereby such reactions asdehydrogenation, isomerization, cyclization and hydrocracking arepromoted. In some cases a minor amount of a halogen, such as chlorine orfluorine, is incorporated in the catalyst to control the catalyticactivity for promoting certain types of these reactions.

In some cases a conventional catalyst of altered characteristics can beused in the present invention. Usually reforming catalysts contain twocomponents each of which substantially provide a characteristicfunction. For example, the cracking function of a platinum-on-aluminacatalyst is substantially provided by the alumina component and thedehydrogenation function is substantially provided by the platinumcomponent. Since, in the present invention, advantage is taken of thepredominance of the dehydrogenation function in the earlier stages ofreforming and the predominance of the hydrocracking function in thelater stages, different, special altered catalysts can be used in therespective stages which catalysts will provide the more desired functionin the respective stages. Thus for eample, a platinum-on-aluminacatalyst with an increased amount of particularly active form ofplatinum can be used in the earlier stages to promote dehydrogenationand a catalyst with an increased amount 4 or particularly active form ofalumina can be used in the later stages to promote hydrocracking.

In the early stages of the reforming, conditions can be varied ratherwidely; thus temperatures of about 600 to about 1050 F. are suitable andthe-preferred range is from about 800 to about 950 F. Within thesetemperature limits weight space velocities of about 0.05 to about 10.0pounds of naphtha, per hour, per pound of catalyst in the reaction zonemay be employed advantageously; however, space velocities of about 0.25to about 5.0 provide the best results. Hydrogen should be introducedinto the reforming reactor at rates running from about 0.5 to about 20.0moles of hydrogen per mole of hydrocarbon reactants. The reactionpressure in the reforming can be maintained between about 50 and about1000 pounds per square inch gauge (p.s.i.g.). Best results are obtainedby holding the reaction pressure within the range between about andabout 750 p.s.i.g.

Referring again to the drawing, the naphtha fraction of boiling range200 to 390 F. is heated in 12 to about 900 F. and is passed 13 into afirst reactor zone 9 into contact with a platinum on alumina catalyst.The zone 9 is maintained at an inlet temperature of about 900 F. andoutlet temperature of about 825 F. The feed is passed to the zone at apressure of about 450 p.s.i.g. and exits from zone 9 at a pressure ofabout 440 p.s.i.g. Hydrogen is recycled 14 to the feed zone 9 tomaintain a hydrogen to oil mole ratio varying between about 3 and 10.

The naphtha fraction is passed from Zone 9 via line 15, is reheated 16to 900 F. and is passed 17 to a second reactor zone 10 wherein thefraction is again contacted with platinum-on-alumina catalyst attemperatures between about 850 to 900 F. and pressures between 390 and415 p.s.i.g.

As per the present invention, conditions in the early stages of thereforming as represented by reactor zones 9 and 10 of the drawing, arecontrolled to produce substantial dehydrogenation of naphthenes. Theproduct of the early stages passes 18 from reactor zone 10 and iscombined with the heavy naphtha fraction of boiling range 390 to 415 F.from line 6. The higher boiling, heavier naphtha fraction of the presentinvention is specifically illustrated in the drawing as a fraction ofboiling range 390 to 415 F.

In the drawing, hydrogen 19 is added to the combined naphtha fractionsin line 20. The combined feed is then heated 21 to about 950 F. and ispassed 22 to later reactor zone 11 of inlet pressure of about 370p.s.i.g. and outlet pressure of 340 p.s.i.g. The temperature in thiszone is maintained at temperatures averaging 50-125 F. higher than thetemperatures in the earlier zones. The later reactor zone is representedin the drawing by a single reactor zone 11 but again this zone cancomprises a plurality of reactors or can comprise a latter stage of asingle reactor in which a complete reforming operation is carried outper the present invention.

Chloride is added to the combined feed to the latter stages asillustrated in the drawing by line 23. This chloride can be, forexample, ethylene dichloride and is added for the purpose of inducingincreased hydrocracking. The chloride is added in the range of 1 to 10p.p.m. based on total naphtha feed to the reactors in the latter stageof the process.

The catalyst utilized in zone 11 can comprise any conventional reformingcatalyst as described supra or an altered catalyst as also describedsupra. The operation in this zone produces a product 24 of increasedoctane. In comparison to conventional operation, which utilizes a feedwith a boiling range below 390 F., the present process produces about a5 volume percent increase in C reformate of characteristics comparableto the product produced in the conventional operation. In comparison toa conventional operation which might use a 200 to 415 F. charge stock,the present invention produces a reformate with a lower end point andhigher octane. This improved reformate is produced without the heavycoking which would characterize a conventional reforming of a 200 to 415F. charge stock.

The invention claimed is:

1. In a process for reforming naphtha in a multiple reactor reformerwhich process comprises: charging a naphtha feed boiling below about 390F. sequentially into each reactor of said reformer to reform said feed;and recovering a product of increased octane number; the improvementwhich comprises: adding a heavy naphtha fraction boiling essentiallythroughout the range of 390 to 415 F. into a later reactor of saidreformer combined with its feedstock in the presence of excess hydrogento thereby increase said amount of product of increased octane number bysubjecting the combined feedstocks to hydrocracking and isomerization.

2. A process for producing gasoline employing in combination a reformingzone and an isomerization-cracking zone comprising: separating a heavynaphtha into a first fraction boiling below about 390 F. and a secondfraction boiling essentially throughout the range of 390 to 415 F.;reforming the first fraction in the reforming zone References CitedUNITED STATES PATENTS 2,908,628 10/1959 Schneider et al. 20865 2,990,3636/ 1961 Evans 208-65 3,242,066 3/ 1966 Myers 208---93 3,392,107 7/ 1968Pfeiferle 20865 3,540,996 11/1970 Maziuk et a1. 208-65 3,394,073 7/1968Strickland 208-65 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 208--64,65, 93

